1. Field of the Invention
The present invention relates to a member which must have excellent high-temperature strength, high-temperature hardness, thermal fatigue resistance, and erosion resistance against molten metal, i.e., a casting mold and, more particularly, to a rapidly solidifying water cooled rotary roll member for a molten metal exposed to a severe thermal fatigue environment.
2. Prior Art
Generally, a normal continuous casting mold and the above water cooled rotary roll must have high-temperature characteristics such as a thermal conductivity for reducing a local thermal stress, a high-temperature strength against a large thermal stress, a high-temperature elongation against a severe thermal fatigue environment, and a high-temperature hardness or erosion resistance against molten metal for preventing erosion on a mold surface caused by erosion during casting because surface quality of a cast product is significantly degraded if erosion occurs. This erosion is significant especially in the water cooled rotary roll and a roll service life is determined by the erosion. Therefore, in order to obtain the above characteristics, a Cu-Cr alloy, a Cu-Zr alloy, or a Cu-Cr-Zr alloy is conventionally used.
Recently, in accordance with needs for higher productivity, casting molds have been used under severe environments. Especially, along with developments in continuous casting techniques such as a electromagnetic stirring technique, a surface temperature of a mold which is in contact with a molten metal has been gradually increased from 300.degree. to 400.degree. C. to 400.degree. to 500.degree. C.
Furthermore, in order to obtain various excellent characteristics, a rapidly solidified thin plate is manufactured by a water cooled rotary roll made of various alloys such as silicon steel. In this case, a surface of the roll is exposed to a high temperature of 500.degree. C. even when the roll is used. In addition, since a molten metal is continuously supplied to the same portion, a thermal stress locally acts, and the same time, the roll which rotates at high peripheral speed of which reaches 2 to 40 m/sec. is locally, frequently, and repeatedly heated and cooled. In a normal continuous casting method, when casting reaches a stable state, both the magnitude and distribution of a thermal stress acting on a mold are maintained substantially constant until casting is completed. However, in the above case, the mold is locally exposed to severe thermal fatigue or thermal cycle fatigue generating conditions.
When the continuous casting mold or the water cooled rotary roll manufactured by a conventional Cu alloy is used under the above severe conditions, a service life of the mold is degraded because the high-temperature characteristics, especially the high-temperature strength, the high-temperature hardness, and the erosion resistance against molten metal are insufficient. Especially for the water cooled rotary roll, this problem is critical in practical applications.
As a result of extensive studies for developing a material which has superior high-temperature characteristics and hence can be used not only as a normal continuous casting mold but also as a water cooled rapidly solidifying roll mold which must have better characteristics, the present inventors have found that a Cu alloy containing 1.3 to 5% (% is wt% hereinafter) of Ni, 0.2 to 2% of Ti, 0.1 to 1.5% of Cr, 0 to 0.5% of Zr, 0 to 1% of Al, 0 to 0.5% of at least one of Fe and Co, 0 to 1.2% of Sn, 0 to 1.2% of Mn, 0 to 1.2% of Zn, 0 to 0.2% of Mg, 0 to 0.2% of P, and 0 to 0.2% of a rare earth element, wherein the remainder of said material has a composition consisting of Cu and unavoidable impurities, has excellent high-temperature strength, high-temperature hardness, high-temperature ductility, heat resistance, thermal fatigue resistance, and erosion resistance against molten metal. The present inventors have also found that when the above Cu alloy is used as a member such as a rapidly solidifying water cooled rotary roll which is exposed to a severe thermal fatigue environment in which a large thermal stress is locally repeatedly produced by contact with a molten metal, a service life of the member is significantly improved to achieve a stable performance for a long time period.
The present invention has been made in consideration of the above findings.